Study On The Influence Of Weak Interlayer On The Stability Of Tunnel Cracked Lining

Cracks are one of the common diseases of tunnel lining.The appearance of cracks will affect the construction and operation of tunnel engineering as well as reducing the safety of lining structure.On the other hand,as a common adverse geological condition,weak interlayer damages the integrity and strength of surrounding rock,and then affects the stability of lining cracks and the bearing capacity of lining.On account of this,based on the engineering background,the present article combines the two problems of"weak interlayer"and"cracked lining"to study the stability of lining with cracked vault and cracked haunch under the condition of surrounding rock with orthogonal weak interlayer passing through tunnel vault.By means of model test,fracture mechanics theory and finite element numerical calculation,the data of surrounding rock pressure,internal force distribution of lining,stress intensity factor of cracks and safety factor of lining bearing capacity under the influence of orthogonal weak interlayer passing through tunnel vault with different dip are obtained.Furthermore,the deformation,stress characteristics and failure mechanism of cracked lining are studied.The main research contents are as follows:?1?Based on the ground-structure model,a tunnel similarity model test device was made,and the progressive loading test of lining with cracked vault and cracked haunch in homogeneous ground and ground with 40°dip orthogonal weak interlayer passing through tunnel vault was carried out.The variation of radial contact pressure between lining and surrounding rock and the distribution of internal force of lining were studied,and then the influence mechanism of weak interlayer on stress of cracked lining was analyzed.?2?The stress intensity factors K_I and K_II of vault crack and haunch crack in ground with 10°to 80°dip orthogonal weak interlayer passing through tunnel vault were calculated by finite element numerical simulation based on the theory of fracture mechanics,and engineering fracture criterion was used to obtain the safety factor of lining crack stability.In the mean while,the stress intensity factors of vault cracks with different depths were calculated.It is found that the dip of weak interlayer and the depth of cracks will affect the stability of cracks together.?3?From the aspect of section bearing capacity,the safety factors of bearing capacity of cracked vault and cracked haunch in ground with different dip orthogonal weak interlayer passing through tunnel vault were calculated,and compared with the safety factors of crack stability,it is found that they have similar laws.At the same time,the distribution law for safety factor of bearing capacity of overall cracked lining was calculated.It was concluded that the distribution of safety factor for bearing capacity of lining is asymmetrical with different dip of weak interlayer.Besides,the bearing capacity of lining with cracked vault is lower than that of lining with cracked haunch.?4?From the aspect of interaction mechanism between surrounding rock,weak interlayer and lining,the results of model test and numerical simulation were combined to analyze the stress characteristics of lining.In view of the most disadvantageous situation of the dip of the orthogonal weak interlayer passing through tunnel vault between 40°and 50°,a simplified strucal-load model of the lining was established,and the deformation,stress and failure mechanism of the lining under the influence of the orthogonal weak interlayer passing through tunnel vault were explained.